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Currently the most commonly recognized genetic cause of obesity is the Prader-Willi syndrome- usually diagnosed early in a child's life. And in addition to causing toddlers to overeat and pack on the pounds, the syndrome also typically leads to mental delay.

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Now University of Florida doctors say early-onset morbid obesity --a form of childhood obesity not yet linked to genetics-- is also associated with lower I-Q scores. Researchers performed mental acuity tests on patients who had Prader-Willi syndrome or early-onset morbid obesity and compared the scores to the test results of their normal weight siblings. Doctors were surprised to find that those who became obese before the age of four and had no identifiable reason for cognitive impairment had an average I-Q about twenty-eight points lower than the sibling control group.

Dr. Dan Driscoll / UF pediatrician and geneticist

"It was surprising when we looked at the early-onset morbidly obese individuals that had no known reason for any cognitive impairment (and we did extensive genetic testing) - their I-Q came out to approximately 78 versus a sibling control of 106."

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Early-onset obesity is not nearly as common as the gradual weight gain and eventual obesity that many American children develop. And researchers believe those who become obese later in childhood, or as adults, aren't at risk for the cognitive impairments noted in the U-F study because their brains are sufficiently developed to fend off the damage. But the research does raise concerns for those who become severely obese as toddlers. That's because a number of study subjects those with early-onset obesity and those with Prader-Willi were found to have brain lesions similar to the ones seen in Alzheimer's patients. Doctors say those changes could be associated with the drop in intelligence scores these children experienced. None of the scans of normal-weight controls, on the other hand, demonstrated those changes. These findings could be affecting food-seeking centers in the brain and causing the children to feel hungrier. However experts say they are more likely the result of obesity-related metabolic changes damaging the developing brain. Experts say more studies are necessary to find the origin of these lesions and to expand the I-Q studies.

Dr. Dan Driscoll / UF pediatrician and geneticist

"We certainly think that there's a strong possibility that the metabolic, biochemical problems associated with obesity could be interfering with normal brain development."

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At the University of Florida Health Science Center, I'm Mike Garrison